There is a paucity of behavioral data and an absence of biological data on autism at 12 months of age. The reason for these major gaps in vital information is because autism remains behaviorally, not biologically, defined and diagnosed. Prospective, hypothesis- driven studies of behavior and biology in autistic infants would be powerful and are essential, but are missing. Currently, the infant sibling design is the only prospective approach in use. This design is strong but also has limitations including high costs, long-time scale, potential for sampling bias, and the heavy demands on the researcher to identify, recruit, and maintain contact long-term with large numbers of mothers and infants. We propose a different prospective strategy, called the 1-Year Well Baby Check-Up Approach, that does not involve any of these limitations. Because most babies see their pediatrician at 1 year, we propose to have 60 pediatricians give a brief screening questionnaire to parents while in the waiting room, the CSBS-DP Infant Toddler Checklist (Wetherby and Prizant, 2002), at every 1-year well baby check-up. Infants whose scores fall outside of the normal range will be referred to us for follow-up diagnostic and psychometric testing. Babies judged to be at-risk for autism or developmental delay (DD) will be followed longitudinally to determine the success rate of this procedure. Control subjects will be babies who score within the normal range on the checklist. Success of this model approach can have an immediate impact on pediatric practice. Babies judged to be at-risk for autism or DD, as well as controls, will participate in two studies aimed at demonstrating that important behavioral and biological information can be obtained via this approach. In one study, to address the important question of immunological abnormality in autism early in life, we will use state- of-the-art methods to assay plasma levels of specific immune significant cytokines and growth factors. In the second study, to address important questions about early social interest and orienting abnormalities in autism, we will use a quantitative experimental procedure for investigating social preference behavior and eye gaze patterns. Successful identification of biological and behavioral features of autism at 12 months of age will have a major impact by introducing the possibility of pediatric referral of high risk infants for quantitative and objective tests that can aid in earlier diagnostic and treatment decisions.7.